1. Field of the Invention
The present invention relates to a liquid injection apparatus for atomizing liquid and injecting the atomized liquid into a liquid injection space.
2. Description of the Related Arts
As such liquid injection apparatuses, a fuel injection apparatus for an internal-combustion engine is known. The fuel injection apparatus for the internal-combustion engine is a so-called electrically controlled fuel injection apparatus comprising a pressurizing pump for pressurizing liquid and an injection valve, and has been widely and practically in use. However, as the electrically controlled fuel injection apparatus is configured in such a manner that the fuel pressurized by the pressurizing pump is injected from the injection port of the electromagnetic injection valve, the droplet size of the injected fuel is relatively large, about 100 xcexcm at minimum, and further the sizes are not uniform. Such large droplet sizes or uneven droplet sizes of the fuel increase incomplete combustion of fuel when the fuel is burned, thereby causing the increase in toxic emission.
On the other hand, as Japanese Patent Application Laid-open (kokai) No. 54-90416 discloses, a droplet eject apparatus is proposed, wherein the liquid in a liquid supply passage is pressurized by operation of a piezoelectric element to produce ultra-fine droplets of liquid and these droplets of liquid are ejected from an eject port. Apparatuses of the type described use the principle of the ink jet eject apparatus disclosed, for example, in Japanese Patent Application Laid-open (kokai) No. Hei6-40030, or others. In the apparatus, the size of the ejected droplet (the droplet of injected fuel) can be reduced and can be uniform, when compared to the above-mentioned electrically controlled fuel injection apparatus. Therefore, this apparatus can be said to be an excellent apparatus in atomizing fuel.
When the ink jet eject apparatus is used under a relatively steady-state environment with less change in the temperature or pressure (for example, in an office room, or school), it can give its intended performance to inject liquid in the form of droplets of liquid. However, if it is used under such an environment that fluctuates heavily caused by fluctuation of operating conditions, like an internal-combustion engine, it is generally difficult for the apparatus to fully give its intended performance to atomize the fuel. Therefore, no liquid (fuel) injecting apparatus has so far been provided which fully succeeds in atomizing liquid and injecting the liquid in the form of droplets of liquid, by means of using the principle of the ink jet eject apparatus, for a mechanical apparatus with heavily fluctuating environment like an internal-combustion engine.
When such a liquid injection apparatus is applied to mechanical apparatuses like an internal-combustion engine, the liquid injection apparatus is required to securely and stably supply the amount of injection of the liquid required by the mechanical apparatus, and at the same time, to inject the liquid at the injection timing required by the mechanical apparatus without delay. However, since such liquids injecting apparatuses carry out injecting by means of increasing or reducing the pressure of liquid, air bubbles are easily formed in the liquid, and if such air babbles are not removed before they become large, the pressure of the liquid cannot be increased as expected. Therefore, the apparatus cannot satisfy the requirements as to the amount of injection and the injection timing.
It is therefore the object of the present invention to provide a liquid injection apparatus capable of stably accomplishing atomization of liquid and injecting the liquid in the form of uniform minute droplets of liquid. Another object of the present invention is to provide a liquid injection apparatus, which is configured to have the capability of stably injecting liquids even under conditions that the use environment for the liquid injection apparatus such as liquid injection space heavily and suddenly fluctuates. A further object of the present invention is to provide a liquid injection apparatus, which can inject the intended amount of injection of liquid at the intended injection timing, by means of preventing air babbles from being formed in the liquid within the liquid injection apparatus.
In order to achieve the above objects, according to a first aspect of the present invention, there is provided a liquid injection apparatus comprising an injection device including a liquid ejection nozzle having one end exposed to a liquid injection space, a piezoelectric/electrostrictive element, a chamber connected to the other end of the liquid ejection nozzle, the chamber having a volume changed by the operation of the piezoelectric/electrostrictive element, a liquid supply passage connected to the chamber, and a hollow cylindrical liquid filling port allowing the liquid supply passage to communicate with the exterior; pressurizing means for pressurizing liquid; an electromagnetic ejection valve to which liquid pressurized by the pressurizing means is supplied, the electro-magnetic ejection valve including a solenoid valve and an ejection hole which is opened or closed by the solenoid valve, the electromagnetic ejection valve ejecting the pressurized liquid through the ejection hole when the solenoid valve is opened; and a hermetically sealed space forming member for forming a hollow cylindrical hermetically sealed space between the ejection hole of the electro-magnetic ejection valve and the liquid filling port of the injection device, the hermetically sealed space having substantially the same diameter as the diameter of the liquid filling port; liquid ejected from the electro-magnetic ejection valve being atomized by change of volume of the chamber and injected in the form of droplets from the liquid ejection nozzle into the liquid injection space, wherein the electro-magnetic ejection valve is configured to eject liquid ejected from the ejection hole in a direction having a predetermined angle relative to a center axis of the hollow cylindrical hermetically sealed space, such that the distance of the liquid from the center axis increases accordingly as the distance from the ejection hole toward the liquid filling port increases.
By virtue of such a configuration, the liquid pressurized by the pressurizing means is ejected from the electromagnetic ejection valve into the injection device, and then the liquid is injected from the liquid ejection nozzle with being atomized by means of volume change of the chamber in the injection device.
In this case, the size of the atomized droplet varies depending on physical properties, such as a pressure to be applied to the liquid, an amplitude and/or a frequency of the vibration caused by the piezoelectric/electrostrictive element, the shape and/or dimension of a flow path, and the viscosity/surface tension of the liquid. However, if the period of vibration applied to the liquid is smaller than the time required for the liquid, in the vicinity of the end portion of the liquid ejection nozzle (the opening exposed to the liquid injection space), to travel by the length equivalent to the diameter of the end portion of the liquid ejection nozzle, the size of the droplet to be ejected is almost less than the diameter of the end portion of the liquid ejection nozzle. Therefore, for example, if the diameter of the end portion (opening) of the liquid ejection nozzle exposed to the liquid injection space is designed to be less than tens of xcexcm""s, the liquid injection apparatus will be able to inject droplets of liquid which are atomized (formed) into extremely uniform small pieces, and, for example, if the apparatus is used as a fuel injection apparatus for an internal-combustion engine, the fuel consumption of the internal-combustion engine can be improved and toxic emission can be reduced, as the apparatus can atomize (form) the injecting fuel into droplets of liquid having an appropriate diameter.
Moreover, according to the above-mentioned configuration, since the pressure required for injecting liquid is generated by pressurizing means, the apparatus can stably inject and supply the liquid in the intended form of very small particles, even if the environment for the liquid injection space (for example, the pressure and temperature) is abruptly changed due to changes in operating conditions for the machine to which the apparatus is applied.
Furthermore, in the conventional carburetor, the flow rate of the fuel (liquid) is determined corresponding to the flow rate of the air in the space within the intake pipe, that is the liquid droplet ejecting space, and the degree of atomization varies depending on the flow rate of the air, however, the liquid injection apparatus according to the present invention can eject only the required amount of the fuel (liquid) which keeps satisfactory atomized state, regardless of the flow rate of the air. In addition, the liquid injection apparatus according to the present invention does not require a compressor for supplying assist air, unlike the conventional apparatuses which promote the atomization of the fuel by means of supplying assist air to the nozzle of the fuel injector. This is one of the reasons for the possibility of embodying the apparatus at low cost according to the apparatus of this invention.
Also, in the above-mentioned configuration, between the ejection hole in the electromagnetic ejection valve and the liquid filling port in the injection device, a hollow-cylindrical hermetically sealed space is formed, which has substantially the same diameter as the liquid filling port, and the shape of which is a hollow cylinder, by the hermetically sealed space forming member, and the liquid from the ejection hole is ejected in the direction having a predetermined angle to the center axis (of the hollow-cylindrical hermetically sealed space), so that the distance of the liquid (droplets) from the center axis of the hollow cylindrical hermetically sealed space increases, as the distance from the ejection hole to the liquid filling port increases.
As a result, as the flow of the ejected liquid is generated in a wide area of the hollow cylindrical hermetically sealed space, air bubbles are particularly hard to stay in corners in the vicinity of the ejection hole in the electro-magnetic ejection valve in the hollow cylindrical hermetically sealed space, or air bubbles formed at the corners are easily and promptly removed, before they become larger. Therefore, in this liquid injection apparatus, since the pressure rise of the liquid is hardly hindered by air bubbles, the pressure of the liquid can be increased as expected, and the apparatus can inject the required amount of droplets of liquid at the required injection timing according to the requirements of mechanical apparatuses.
In this case, the preferred angle formed between the flow line of the droplets of liquid ejected from the eject port and the axis of the hollow cylindrical hermetically sealed space, i.e., the predetermined angle xcex8 is preferably 5xc2x0 or more and 30xc2x0 or less.
In other words, if the predetermined angle xcex8 is smaller than 5xc2x0, since fluid (including air) is easily stay at corners in the vicinity of the electro-magnetic ejection valve in the hollow cylindrical hermetically sealed space, air bubbles are easily formed at the corners, and on the contrary, if the predetermined angle xcex8 is larger than 30xc2x0, the substantial traveling distance of the liquid ejected from the ejection hole till it arrives at the liquid supply passage becomes long, thereby retarding the rise of the liquid pressure in the liquid supply passage, and consequently making it difficult for the ejection nozzle to inject droplets of liquid at the intended injection timing.
Preferably, by the time when liquid ejected from the electromagnetic ejection valve is injected through the ejection nozzle into the liquid injection space, a flow of the liquid is bent at substantially right angles at least once.
Such a configuration can be embodied, for example, by means of arranging a liquid filling port and a liquid supply passage such that the flowing direction of the liquid which passes through the liquid filling port intersects the flowing direction of the liquid which passes through the liquid supply passage at right angles, and also arranging the liquid supply passage and a chamber such that the liquid which passes through the liquid supply passage is introduced into the chamber after being bent at generally right angles, or arranging the chamber and the ejection nozzle such that the liquid which passes through the chamber is bent at generally right angles and flows into the ejection nozzle.
According to configurations of the type described, as the flow of the liquid ejected from the electro-magnetic ejection valve is bent at generally right angles at least once, the pulsation of the liquid pressure within the injection device incidental to the opening operation of the electro-magnetic ejection valve is reduced, and/or the distribution of liquid pressure in the injection device becomes equalized (the liquid pressure is distributed equally), the apparatus can stably inject droplets of liquid. Especially, when the injection device has a plurality of chambers connected to a common liquid supply passage, if the flow of the liquid ejected from the electro-magnetic ejection valve is bent at generally right angles by the liquid filling port and the liquid supply passage, the pressure of the liquid within the liquid supply passage will be stabilized, and the pressure of the liquids within the individual chambers will also be stabilized, thus resulting in acquisition of equal sizes of droplets of liquid ejected from the ejection nozzle connected to the chambers.
The liquid supply passage preferably includes a plane section which is opposed to (confronts) a virtual plane defined by a section at which the liquid supply passage is connected to the liquid filling port, the plane section extending in parallel with the virtual plane, and the electro-magnetic ejection valve is preferably arranged such that an ejection flow line of liquid ejected from the ejection hole intersects the plane section of the liquid supply passage without intersecting a side wall of the hollow cylindrical hermetically sealed space formed by the hermetically sealed space forming member, or a side wall which is created by virtually extending the side wall of the hermetically sealed space down to the plane section of the liquid supply passage.
According to this configuration, as the liquid ejected from the electro-magnetic ejection valve arrives at the plane section of the liquid supply passage with keeping its kinetic energy (flow velocity) in high state, the liquid is strongly reflected in the plane section toward the filling port and the vicinity side of the ejection hole in the hollow cylindrical hermetically sealed space formed by the hermetically sealed space forming member. As a result, since the flow of the reflected liquid can remove air bubbles staying at corner sections in the vicinity of the ejection hole in the hollow cylindrical hermetically sealed space, the amount of air bubbles in the liquid can be reduced. Accordingly, in the liquid injection apparatus, since it will be much more difficult for air bubbles to hinder the rise of the liquid pressure, and the pressure of the liquid can be increased as expected, the liquid injection apparatus can inject the specified amount of liquid in the form of droplets of liquid at the specified injection timing, as mechanical apparatuses require.
Preferably, the ratio (V/Q) is 0.03 or less where V represents a volume (cc) of a liquid flow passage extending from the electro-magnetic ejection valve (portion of the ejection hole) up to the leading end of the ejection nozzle of the injection device, and Q represents the quantity of ejection per unit time (cc/minute) of liquid ejected from the electromagnetic ejection valve.
Here, the fluid volume formed from the electro-magnetic ejection valve to the leading end of the ejection nozzle of the injection device means the total volume of the hermetically sealed space for the hermetically sealed space forming member, liquid filling port, liquid supply passage, chamber and liquid ejection nozzle (in the case where the liquid supply passage and the chamber are connected with a liquid introduction hole, the volume of the liquid introduction hole is included in the total volume).
The reason for setting the size of the ratio (V/Q) as described above, is that if the ratio (V/Q) is larger than 0.03, the volume V (cc) becomes excessively large to the flow rate Q (cc/minute), and the time period between the timing when the device starts ejecting the liquid by the electro-magnetic ejection valve and the timing when the pressure of the liquid within the ejection nozzle in the injection device starts rises becomes too long, thereby causing a difficulty in injecting droplets of liquid at the intended timing.
In order to attain the above objects, according to a second aspect of the present invention there is provided a liquid injection apparatus comprising an injection device including a liquid ejection nozzle having one end exposed to a liquid injection space, a piezoelectric/electrostrictive element operated by a drive voltage signal, a chamber connected to the other end of the liquid ejection nozzle, the chamber having a volume changed by the operation of the piezoelectric/electrostrictive element, a liquid supply passage connected to the chamber, and a liquid filling port allowing the liquid supply passage to communicate with the exterior; pressurizing means for pressurizing liquid; an electromagnetic ejection valve to which liquid pressurized by the pressurizing means is supplied, the electro-magnetic ejection valve including a solenoid valve driven by a valve drive signal and an ejection hole which is opened or closed by the solenoid valve, the electro-magnetic ejection valve ejecting the pressurized liquid through the ejection hole into the liquid filling port of the injection device when the solenoid valve is driven; and an electric control unit including drive voltage signal generation means for generating the drive voltage signal, and valve drive signal generation means for generating the valve drive signal; liquid ejected from the electro-magnetic ejection valve being atomized by change of volume of the chamber and injected in the form of droplets from the liquid ejection nozzle into the liquid injection space, wherein the electric control unit is configured to start generating the drive voltage signal at a point of time prior to the time when the pressure of liquid within the liquid supply passage starts to rise as a result of generation of the valve drive signal.
By virtue of this configuration, at the instant when the pressure of the liquid within the liquid supply passage starts rising by the generation of the valve drive signal, i.e., at the instant when the ejection nozzle in the injection device likely starts injecting droplets of liquid, the piezoelectric/electrostrictive element is already driven by the drive voltage signal, and oscillation energy (vibration energy) is added to the liquid, therefore, the device can securely inject atomized droplets of liquid from the beginning of injecting liquid.
Similarly, according to a third aspect of the present invention, the electric control unit is configured to continue generation of (i.e. to generate) the drive voltage signal till a point of time posterior to the time when the valve drive signal comes to an end.
By virtue of this configuration, since the pressure of the liquid within the liquid supply passage is kept higher than the pressure required for injecting for a while even after the valve drive signal is ended, at the instant when the ejection nozzle in the injection device keeps injecting droplets of liquid, the piezoelectric/electrostrictive element is still driven by the drive voltage signal, and oscillation energy is still applied to the liquid. Therefore, the device can securely atomize and inject the liquid, (until the injection actually stops) even after the valve drive signal is ended.
Preferably, the injection device comprises a plurality of the liquid ejection nozzles such that the directions of injection of liquid droplets injected from the plurality of liquid ejection nozzles are parallel to each other.
According to this, the droplets of liquid ejected from the individual ejection nozzle to the liquid injection space will not cross each other, so that droplets of liquid can be prevented from becoming large by colliding with each other, and the satisfactory atomizing state of injecting droplets of liquid can be maintained.